Control system of the correspondence kind for movable members



Jan. 15, 1952 F. H. BELSEY HAL 2,582,222

common. sYsrsu OF THE CORRESPONDENCE KIND FOR MOVABLE mzussns Filed Dec. 24, 1948 2 SHEETS-SHEET 1 I Fi .l. I I

I f I WM/H:

rDii 2* Thew- Attorney.

1952 F. H. BELSEY ET'AL 2,582.222

CONTROL SYSTEM OF THE CORRESPONDENCE KIND FOR MOVABLE MEMBERS Filed Dec. 24, 1948 2 SHEETSSHEET 2 Inventors: Frederick H. Belsey, David T. Broadbent,

Their Attorney Patented Jan. 15, 1952 CONTROL SYBTEI OF THE OOBBIBPOND- INCE KIND I03 MOVABLE mans www.mmn-mmm Mata-ignore nuance Stretf New York Company, a mention aamass mom-aural lerlallioJ'lM lnflroath'ltahm'hlm 1 Claims. (01. 81H.)

1 This invention relates to control systems of the correspondence kind, that is to say control systems for maintaining a movable member in a required position corresponding with that of a fixed or movable controlling member or object, such as in alignment with a control member. Control systems of this kind comprise means responsive to departure of the position or motion of the movable object from the required position or motion thereof, producing a control action on.

a motive equipment or source of power for moving the movable object, whereby to produce on the latter a torque directed to reduce said departure to zero, so as to maintain the required correspondence between the positions or motions of the movable member and the controlling member or object.

The invention moreover relates specifically to correspondence control systems of the kind in which said control action is responsive to the velocity of the movable member; such velocity control may be the primary means by which the required motion of the movable member is maintained or may be additional to a control action dependent upon displacement of the movable member from the required position thereof, the control in accordance with velocity being then employed to stabilize the system against hunting, namely self-sustained or lnsufliciently damped oscillation, of the movable member about the required position thereof at any time. Copending application Serial No. 65,708, having a similar title, filed December 16, 1948, in the names of the present inventors, describes arrangements of positional correspondence control systems in which the control action dependent upon the displacement and velocity of the movable member instead of being derived directly from the movement of the movable object alone, comprises two components derived respectively from themovements of the movable member and the motive equipment therefor. As described in said specification these arrangements provide advantageous opera,- tion in reducing the detrimental eifects on the correspondence control of resilience and backlash which may be present in the drive-from the motive equipment to the movable member.

According to the present invention, in a control system of the correspondence kind, as generally hereinbefore defined means are provided responsive to relative velocity between the motiveequipment and the movable member forproducing control actions dependent on the velocities of both said member and said motive e ipm nt. and reducing the resultant effect of said control actions for a given velocity of the motive equipment independently of corresponding velocity of the movable membe as a result of backlash or resilience in the drive between said equipment and said member, as compared with movement of the motive equipment and movable member at corresponding velocities to one another. The arrangement therefore provides as regards control in accordance with velocity of the movable member similar advmtages in improving the stability of the control system as are provided by the system according to the aforesaid copending application.

In carrying out the invention the control system may, according to one form, comprise means responsive to the velocity of the movable memberand means responsive to the velocity of the motive equipment, in combination with means adapted to produce a control quantity representative of the required velocity of the movable member; said velocity responsive means producing respective control quantities dependent on the velocities of the movable member and motive equipment are arranged to act in the same sense as one another for movements of the motive equipment in the direction corresponding to movement of the movable member. The velocity responsive means may conveniently comprise tachometer generators coupled respectively with the movable member and the motive equipment and connected, in series with a tachometer generator or other means producing a voltage dependent on the required velocity of the movable member, in the input circuit of electrical control means governing the operation of the motive equipment.

According to another form, the control system may comprise, in addition to means responsive to the velocities of the movable member or the motive equipment therefor with respect to the required velocity, further means differentially responsive to the velocities of the movable member and the motive equipment, and producing an additional component in the control quantity ap plied by said first means to control means for governing the operation of the motive equipment. The means differentially responsive to the relative velocities of the movable member and the motive equipment may conveniently comprise tachometer generators coupled respectively with said movable member and motive equipment. and connected in circuit with one another to produce a voltage or current dependent on the diilerenee between the speeds of said generators,

control means being provided for producing on the motive equipment a control action comprising two components. one dependent on said current or voltage and the other dependent on departure of velocity of the movable member or the motive equipment from the required velocity. Said means responsive to departure of the velocity of the movable object or of the motive equipment from the required value may for example comprise a tachometer generator havin co-operating elements coupled respectively with the movable member or the motive equipment and with a control member with which the movable member is required to be maintained in velocity correspondence.

Preferably, in carrying out the invention, the control system includes adjustable means for varying at will the relative proportions of the control action derived from the velocities of the movable object and the motive equipment respectively.

According to another feature of the invention, the ratio between the magnitude of the component of control action derived from the velocity of the movable member to the sum of the two components dependent on the velocities of the movable member and the motive equipment is made or adjustable to a value equal or substantially equal to It. ri' u where I1. is the moment of inertia of the load expressed at the motor shaft, namely the moment of inertia of the load divided by the squareof the velocity ratio between themotive equipment and the load. and In is the moment of inertia of the motive equipment. In carrying out the invention,'the control system is preferably arranged so that said ratio may be readily adjustable within limits so as to provide optimum operation.

As hereinbefore indicated the system according to the invention may be of the kind in which velocity alone of the movable member is controlled or may be of the kind in which the response to the velocity of the control member is additional to control in accordance with the displacement of said member. In other words, the means responsive to velocity are additional to means responsive to misalignment of the movable member from the required position thereof, the control means for the motive equipment being jointly responsive to control actions produced by voltage. It will, however, be understood that the invention is not limited in this respect but may,

said velocity responsive means and said misalignment responsive means. In the application of the invention in systems of the latter kind the control responsive to the displacement may be arranged to depend on both the displacement of the movable member and the motive equipment to provide resetting operation in accordance with said foregoing copending application" Two embodiments of control system according to the invention will now be described by way oi. example with reference to Figs. 1 and 2 respectively of the accompanying drawings, which show the arrangements diagrammatically. In these embodiments the control system is of an e1ectrical.

with suitable modifications, be employed in con- Junction with power equipments of any desired kind and with control elements of an other desired form than electrical.

Referring first to Fig. 1, the embodiment of the invention therein shown is applied to a control system in which the motion of a hand-wheel or other control member 1 determines the motion of a movable member 2 or load device. This movable member is driven by a motive equipment which in the example illustrated comprises a direct current electric motor 3, the armature of which is connected by conductors 4 and 5 in the output circuit of a cross-field or armature reaction generator 6, preferably of the metadyne kind. This generator has a controlling field winding 1 connected in the output circuit of an amplifying means 8 arranged to produce by means of the field winding 1 a controlling field in the generator 6 dependent as will hereinafter be described on voltages applied to a pair of conductors 9 and I0 and a pair of conductors II and I! with corresponding control of the output current of the generator 6 and of the torque of the motor 3 which may be provided with a separately excited field winding i3.

Resilience or backlash, or both, present in the transmission between the motor 3 and the load 2 is indicated diagrammatically at ii.

The velocity control means according to this embodiment of the invention comprises three tachometer generators IS, IS and il, coupled respectively with, and producing voltages dependent on the velocities respectively of, the control member l,-.the motor 3, and the movable member or load 2. The tachometer generators l6 and i! have their output terminals connected respectively with the resistances of two potentiometers l8 and [9. The moving contacts 20 and 2| of these potentiometers are connected electrically together and may also be mechanically connected as indicated at 22 so as tomove in union with one another. One end of the potentiometer resistance l8 is'connected by a conductor 23 with one output terminal of the tachometer generator l5 whilst one end of the other potentiometer resistance i9 is connected with the input conductor [2 of the amplifying means 8, the other input conductor ll of which is connected with the other output terminal of said tachometer generator 15.

The control system also includes a transmitter element l3 in the form of a selsyn device coupled with the control member I and interconnected electrically by conductors 29', 30' and 3| with two resetting elements comprised by further selsyn devices [6 and 26 coupled respectively with the motor and load. The rotor winding ll of the selsyn I3 is connected with the same source of alternating current as are the input conductors i3" and ll" of the amplifier 8. The rotor windings 23' and 32' of the selsyns l6 and 26 are connected by conductors 33, 34', 31' and 38 with respective potentiometers 35' and 36', the variable voltage output terminals of which are connected in series for the two potentiometers between the conductors 9 and in. The various parts designated in Fig. 1 by primed reference numerals correspond respectively with the several parts designated by like unprimed reference numerals in Fig. 1 of the aforesaid copending application, and these parts opprateto produce between the input conductors I and II an alternating voltage the magnitude and sense of which in relation to the alternating voltage applied to the rotor winding II and the conductors l8 and II is dependent upon misalignment of the movable member I from the required position of correspondence with the control member i, said voltage comprising components dependent respectively on the displacements of the movable member I and of the motor I. the proportion between which components is adjustable by the movable contacts II and II of the potentiometers in a manner fully described in said copending application to which reference is hereby directed.

The amplifier I in Fig. 1 comprises a first stage consisting oi two thermionic valves II and It the control grids of which are connected through secondary windings II and Ila, of an input transformer, the primary winding II of which is connected with the conductors I and iI. with tapping points II and Ila of a centre tapped potentiometer resistor II, which is connected between the conductors ii and i2, automatic grid bias being provided by usual means at II. The anode circuits of the valves are energised from conductors II" and II" through transformers 31 and II with alternating voltages in opposite phase to one another. The amplifier may include one or more further stages by which the resultant excitation of the field winding 1 of the generator I is made to depend upon the difference between the anode currents of the two valves Ill and It. Smoothing means will be provided in the amplifier circuits for smoothing the field current of the generator I. Such smoothing means and further stage or stages, which may be arranged in any suitable manner as will be apparent to those skilled in the art, are indicated diagrammatically at Ia.

As hereinbefore indicated, in this embodiment of the invention there are produced at the input transformer secondary windings 32 and 32a alternating voltages which in themselves tend to maintain the movable member in alignment with the control member I. The tachometer generators l6 and il produce voltages which are dependent respectively on the velocities of the motive equipment and the movable member. A proportion of each of these voltages is applied to the input circuit of the amplifier in opposition, for velocities of the motor and movable member in the same direction as the velocity of the control member, to a voltage dependent on the velocity of the control member produced by the tachometer generator IS. The proportion oi the voltages derived from the tachometer generators II and i1 is adjustable by movement of the contacts and II of the potentiometers iI and II. These potentiometers are adjusted so that when the motor and load move together without backlash or resilience therebetween then the sum of the voltages derived from the two potentiometers, namely between the conductors 23 and II, will be equal to the voltage produced by the tachometer generator It for a corresponding velocity of the control member I. The mechanical connection of the contact points 20 and II will provide for this adjustment of the proportions of the two voltages derived from the potentiometers. The direct current voltage produced between the conductors II and i! in dependence on the velocities as Just above set forth is added in the grid circuits to the alternating voltage derived from the input transformer, namely from the conductors I and II, so that the difference between the anode currents of the two valves willproduce a resultant excitation of the generator field winding 1 containing two components dependent respectively on the displacements and velocities of the movable member and load with respect to the control member.

It will be understood that whereas in the arrangement shown in Fig. 1 of said copending application, the control in accordance with the velocities of the control member and movable member and motive equipment is derived from the rate of change of the voltage dependent on the displacements of said members and motor by appropriate arrangement of the amplifier circuits, in the arrangement shown in Fig. i the amplifier I need not include such means for modifying the effect of the displacement responsive voltages. The first stage of the amplifier I is generally similar to that of the amplifying circuit arrangements shown at C and D in Fig. l of the cognate specification of application for British Letters Patent No. 592,208 (U. 8. Serial Nos. 610,353 and 610,356, now Patents Nos. 2,536,876 and 2,528,488, respectively) to which reference is made for a fuller description of the operation of said stage.

It will be understood that the tachometer generators II, II and il may be coupled with the motor and movable member through appropriate gear trains, but these gear trains since they have to transmit only a small torque for driving said generators may be made to operate without appreciable backlash.

Fig. 2 shows another embodiment of the invention, representing a modification of the arrangement shown Fig. 1 for use in a system in which the control of the movable member in accordance with a control member is obtained from the motion 01' the movable member with respect to the control member, a quantity representing such motion being in certain control systems the only available quantity by which the required control can be obtained, such as, for example, in cases where the control member comprises a gyroscopic device for stabilising the movable member against movements oi a supporting structure, for example the deck of a ship. Fig. 2 illustrates a modification according to the present invention of a gyroscopic stabilised system generally in accordance with Fig. 3 or Fig. 4 of the copending application. In Fig. 2 the motor is again indicated at I with its field winding at II whilst tne movable member, such as the platform above referred to, is indicated at 2 being coupled with the motor through a transmission involving resilience or backlash or both at It. The control member in this case comprises agyroscope designated 64'. At It and 28' are shown respectively a pair of selsyn devices corresponding with the devices IG and 28 of Fig. 3 and Fig. 4 of the earlier application aforesaid, and a device i3 having co-operating elements coupled the one through gears Ill and II with the load 2 and the other through gears 42 and II with the gimbal cage of the gyroscope II: this device is arranged to produce a control quantity dependent upon misalignment between the load 2 and the gyroscope II and may be either the selsyn device I! of said Fig. 3 or the equivalent device II of said Fig. 4.

The devices II, 26' and II are connected in a circuit governing the voltage applied to input conductors I and ll of the amplifier I, this circult arrangement being that shown in said Fig. 8 or Fig. 4 and therefore not being illustrated or further described in connection with Fig. 2 of the accompanying drawings. It will be understood that the amplifier 4 of Fig. 2 is arranged as described with reference to Fig. l or the accompanying drawings.

In accordance with the .present invention, tachometer generators is and ii are coupled mechanically with the motor 3 and the load 2 as in Fig. l, and a third tachometer generator 44 has one its elements. for example the field system, coupled by a gear wheel 45 and the gear wheel 4| with the load 2, and its other element. for example its armature, coupled through a gear wheel 48 and the gear wheel 44 with the gyroscope 84'. This tachometer generator will therefore produce a voltage which is proportional to the relative velocity between the load I and the gyroscope 64'.

The armatures of the tachometer generators i4 and II are connected in series in the circuit shown, including the resistance 41 or a potentiometer, one end of which is connected by the conductor 48 with one brush 0! the tachometer generator 44. The input conductor ll of the amplifier 8 is connected with the variable tapping point 48 or the potentiometer 41 .whilst the input conductor i2 is connected with the other brush of the tachometer generator 44.

The voltage applied to the potentiometer 41 is the algebraic difference or the voltages generated by the tachometer generators I6 and i1, these voltages being regarded as of the same sense for velocities of the motor and load in directions corresponding to one another whilst the voltage. derived from this potentiometer is added algebraically to that derived from the tachometer generator 44. The voltages generated by the generators l4 and II are equal to one another when the velocities of the motor and load are equal to one another, having regard to the gear ratio between the motor and the load, so that said voltage will be zero when the motor and load move together without backlash or resilience. The arrangement is such that the voltage derived from the potentiometer 41 will act in the same direction as that derived from the tachometer generator 44 when the motor moves with respect to the load within the backlash or resilience of the transmission in the same direction as movement of the load.

It will now be shown that the arrangement according to Fig. 2 provides identical operation to that of the arrangement 01' Fig. 1. In the operation of the arrangement of Fig. 1 the voltage input in the grid circuit 0! the amplifier is proportional to:

where In the arrangement according to Fig. 2 the voltage generated by the tachometer Ienerator 44 is, using the same notation as for Fig. 1, equivalent to Vl-Vs.

The voltage applied by the tachometer generators l4 and H to the potentiometer 41 is equivalent to VL-VI and the voltage derived from said potentiometer between the conductors Ii and 48 is equal to (1-z) (Vz.Vu), 2 being the displacement 0! the moving contact 4! irom the extreme left-hand or maximum output voltage position. The total voltage derived from the velocities oi the three generators is the algebraic sum oi the last mentioned voltages and that derived from the generator 44. namely:

Vl-Vs-i- (1 z) (VL-VI) =Vl- [zVs-i- (1 -z) VI] which is identical with Expression 1 above so that identical eflects on the operation of the systemare obtained in both embodiments of the invention.

It will be understood that although in Fig. 2 the generator 44 has its co-operating elements coupled respectively with the gyroscope 84 and with the load 2, the arrangement may be modifled by connecting the one element of said generator with the motor 3 instead of the load 2, such arrangement corresponding with that shown in Fig. 4 cl said copending application for the misalignment responsive means. Where the arrangement is modified in this manner the voltage derived from the potentiometer 41 will be arranged to act in opposition to the voltage derived from the generator 44 when the motor is moving with respect to the load, within the limits of the backlash or-resilience, in the same direction as the movement of the load. In general, therefore, the means co-operating with the movable member are arranged to produce a control quantity dependent on the departure of the velocity of the movable member from the required value. to which control quantity is added algebraically a control quantity dependent on velocity or the motive equipment with respect to the movable member, or alternatively means co-operating with the motive equipment are arranged to' produce a control quantity dependent on departure of the velocity of the motive equipment from the required value, from which control quantity is subtracted algebraically a control quantity dependent on the velocity oi! the motive equipment with respect to the movable member.

The advantages of deriving the control action dependent on the motion of the movable member partly from the motion or said member and partly from the motion of the motive equipment are fully set forth in said'copending application to which attention has hereinbei'ore been directed but may be briefly explained by considering the coupling between the motive equipment and the movable member to comprise pure resilience. In such case if the movable member were disconnected from its associatedcontrol element or the correspondence control system and the two control elements then operated to produce a control action imitating the response to a, sinusoidal]! varying displacement of the movable member with respect to its desired position, then the motion of the motive equipment and the movable member will comprise in addition to sinusoidal components having an in-phase relation to the corresponding sinusoidal components in said control action, as would be obtained with a rigid coupling having no resilience, sinusoidal components, having an anti-phase relation to the compensating components in said control action. For frequencies or such sinusoidal components 9 8,508,888 atorneartheresonantire uencyodtheinartia.

oithemovablememberandtheresilieneeoitbe coupling such anti-phase components become very large in relation to the in-phase condition and will have a predominant eil'ect on the periormance oi the control system and the result is that in normal operation instability oi the complete control system may result. Assuming the resilient coupling comprised a long uniform shaft there would be a node at some point along the length oi the shait where the anti-phase components on the two ends of the shaft, namely the anti-phase components in the motions oi the motive equipment and the movable member would neutralise each other, only the in-phase components remaining. It will be clear that ii the control action dependent on the velocity of the movable member were derived from said node the control action would be identical to that with an infinitely stifi' coupling between the motive equipment and movable member. In practice it will not generally be expedient or even possible to derive such control action from a nodal point;

--in general the coupling will comprise a complicated gear chain in which no nodal point is available. With the arrangement according to said copending application. such nodal point is simulated by combining control actions dependent in appropriate proportions on the movements of the motive equipments and the movable member, or in other words on the movements of the two ends 01' the coupling.

The present invention provides similar advantages for the control in accordance with the velocity of the movable member and in similar manner to that provided by the cuts of the earlier application enables the unstabilising streets of resilience between the motive equipment and movable member to be eliminated or reduced from the control system so that more rapid response of the movable member to movement of the control member or, in general, a greater stifi-' ness of the system against departure of the movable member irom the required position or motion thereof, to be obtained. Broadly similar efiects arise in the case of backlash in the transmission so that the present invention provides means whereby the stability of the control system may be improved where backlash or resilience or both are present. In practice, the proportion of the control in accordance with velocity derived from the movable member is most readily determined by experiment, but it will be found that the optimum value of said proportion will correspond very nearly to the inertia ratio s IL+II hereinbeiore set forth. It will be seen that said ratio of control is readily adjustable in the arrangements oi Fig 1 by means of the potentiometers II and I9, and in Fig. 2 by means of the potentiometer ll. a

It will be understood that each of the several embodiments oi the invention above described may be employed in combination with any other desired control means governing the operation oi the motive equipment, of electric or other term, in accordance with the output from the selsyn devices, such as, iorexample, with a hydraulic engine governed by the electromagnetic device described in the complete specification of application for Letters Patent Serial No. 592,208

(British application for Letters Patent No. 22,235

whatweclaimasn wanddesiretosesureby Letters Patent 01' the United States is:

l. A control system comprising, a motor, a mainloadmcmberadaptedtobedrivenbysaid motor, driving connections between said motor and said member, velocity responsive means directly coupled to said member, velocity responsive'means directly coupled to said motor independently oi said member, a control member means for governing the operation oi said motor, and means serially combining the outputs of said velocity responsive means and said control member to produce a control quantity for said governing means.

2. A control system comprising, a motor, a mainloadmemberadaptedtobedrivenbysaid motor, driving connections between said motor and said member, a pair of tachometer generators adapted to produce a control quantiw in accordance with their'respectlve velocities, one of said generators being coupled to said member. the other oi said generators being coupled to said motor independently of said member, a controlling member having a tachometer generator coupled thereto, and means for applying the algebraic sum of the outputs oi said generators to govern the operation 0! said equipment.

3. A correspondence control system as donned in claim 2 further comprising, poten connected to each of said generators to vary the relative proportion of their outpuil.

4. A correspondence control system comprising, motive equipment, a main load member adapted to be driven by said equipment, driving connections between said equipment and said member, a control member adapted to produce a control quantity dependent upon its velocity, velocity responsive means including a pair 01' control elements, one of said elements being coupled with said load member, the other of said elements being coupled to said equipment independently of said load member, each of said velocity responsive means producing a control quantity dependent upon its velocity, and means responsive to all said control quantities for governing the operation of said quipment.

5. A control system comprising, motive equipment, a main load member adapted to be driven by said equipment, driving connections between said equipment and said load member, velocity responsive meam coupled to said load member, velocity responsive means coupled to said equipment independently of said load member, a control member for producing a first control quantity depending upon its velocity of movement. means for combining the output of said velocity responsive means with said control quantity to produce a first resultant control output, means responsive to misalignment of the load member with respect to said control member, means responsive to miralignment of the motive equipment with respect to said control member, means for combining the outputs of said t responsive means to produce a second resultant control output, and means responsive to the algebraic addition of said resultant control outputs for governing said motive equipment.

6. A control system in accordance with claim 5 wherein said control member further comprises, a gyroscopic position stabilizing device.

7. A control system comprising, a motor, a movable member, driving connections between said motor and said movable member, two selsyn 11 4. elements each directly connected to said ""otor and said member respectively, a transmitter selsyn interconnected with said two selsynelements, said elements being adapted respectively to produce a control quantity depending upon the displacement of said motor and said movable Number nrzrnnnnces crrrzn The, following references are of record in the 5 file oithis patent:

UNITED STATES PATENTS Name Date 2,172,410 R1885 -1 Sept. 12, 1939 2,414,480 Nisbet Jan. 14, 1947 2,486,208 -Crever Feb. 17, 1948 2,444,813 Cunningham July 6, 1948 2,457,330 Toner. Dec. 28, 1948 2,587,088 Peoples Jan. 9. 1951 FOREIGN PATENTS Number 1 Country Date 610,028 Great Britain Oct. 11, 1948 

